1. Field of the Invention
The present invention relates to a method of detecting a specified object in an image signal and more particularly to a detecting a specific object in a moving picture file.
2. Background of the Related Art
Recently, technology for digital image signal processing has been greatly developed and has been applied in various fields. For example, the digital image signal processing technology may be used in a search system for automatically editing only the face of a specific character in a moving picture file of a movie or drama, or in a security system for permitting access to only persona registered in the system. The performance of such systems basically depend on the accuracy and speed of the detecting a desired object. Accordingly, various methods of detecting a desired object have been proposed in the related art.
In xe2x80x9cPedestrian Detection Using Wavelet Templatesxe2x80x9d, CVPR97, June 17-19, MIT, a face is detected by using predetermined face templates of a plurality of characters, templates for each character ranging from a minimum size to a maximum size. When the image signal is input to the system, the frames are scanned and matched with the face templates of various size and character to detect the face. As a result, a great number of template matching may be required, thereby increasing the processing time for detecting a desired object.
In xe2x80x9cAutomatic Extraction of Face from Color Reversal Film using Statistical Multistep Techniquexe2x80x9d, ACCV ""95 Second Asian Conference on Computer Vision, December 5-8, a method of detecting the face region of a character in a still image has been proposed. According to this face detecting method, the values expressed in the RGB (red, green, blue) color space are converted to the HSV (hue, saturation, value) color space, and the pixels representing a skin color are detected. Thereafter, segmentation of the detected skin color region is performed using an edge detection, hole filling, and gap filling operation. Thus, a final face region is detected by identifying the face region of a desired character using patterns prepared for estimating the detected region.
However, the relative accuracy of face detection is lower in comparison to other face detection methods because a still image is used which requires less information than the moving image. Also, this method utilizes only skin color information in detecting the face region, but such skin color information may changes according to the ethnic origin and circumstances such as the illumination, background, or makeup state of the character. Moreover, since the method requires the conversion from the RGB to the HSV color space, more processing time is required in detecting the face region.
Other detection methods include automatically detecting the face region of a character if the character moves on a screen of a video camera and then identifying the character if the detected face has been registered. According to this type of face detection, the whole movement of a character is detected using an image difference, and the face of the character is identified using the nervous system. Movements caught by the image difference may include movements of parts such as the body, arms or legs rather than the face, or noises belonging to the background. Thus, accuracy may not be high in detecting the face region from the image which moves as a whole. Also, in case of fast movement of a character, a significant time would be required to detect the face region.
Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art.
An object of the present invention is to provide a method of detecting a specific object in an image signal, both efficiently and accurately.
Another object of the present invention is to provide a method of detecting the face of a character in an image signal, both efficiently and accurately.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purposes of the invention, as embodied and broadly described herein, the method for detecting a specific object in an image signal comprises detecting the specified object using an image difference obtained from two sequential input image frames of a first time difference; detecting a position of a particular feature of the specific object using a second image difference obtained from two sequential image frames of a second time difference which is relatively shorter than the first time difference, and detecting the specific object using a relationship between the specific object and the feature of the specific object; and determining the detection result as a final face region if one detection result of the specified object exists, and determining the final face region by combining the plurality of detection results if a plurality of detection results exist.
According to the present invention, the position of the face can be efficiently and accurately searched using the image differences with respect to movement of an object such as the face and movement of a particular feature of the object such as the eye or mouth. Accordingly, the method of the present invention can be applied to systems such as a moving picture search system or a security system for an effective detection of the face region.